1. Technical Field
The present disclosure relates generally to the fabrication and design of polymer substrates that are photo-sensitive and therefore can be patterned using photolithography, and in particular, to testing media used for DNA and RNA hybridization and evaluation.
2. Description of the Related Art
A DNA bead-type microarray is a solid platform having a top surface in which an array (typically a 2-dimensional grid) of wells is formed to support DNA samples for genetic experimentation and analysis. The DNA samples can be attached to spherical beads that fit into hemispherical- or cylindrical-shaped wells. The bead surfaces are engineered with a chemical matrix to which DNA proteins can attach by covalent bonding. Single helical strands of synthesized DNA (i.e., DNA fragments) called probes can therefore be loaded onto a set of beads. Then, genetic samples, or targets, also single helical strands of DNA, carrying chemiluminescent markers, can be introduced to the probes to determine which of the target genes bind strongly with the probe genes. Strongly bonded, or “hybridized” pairs of genes, form a fully complimentary double helix structure. A subsequent washing step clears away weakly bonded, or non-hybridized, pairs, leaving behind the hybridized pairs of genes. The hybridized genes, now carrying the markers, can then be scanned and imaged for evaluation.
Use of bead-type microarrays entails placing the beads into the wells and retaining them in place during the hybridization procedure, the subsequent washing step, and the imaging step. Consistent fabrication of the substrate and the beads is necessary to properly control DNA and RNA hybridization experiments. Typically, the top surface of the microarray is made of a rigid material such as glass; commonly used materials for the beads are silica, zirconium, polystyrene, or glass. The beads and the wells typically have a diameter within the range of about 0.5-1.0 micron, and rows of wells in a microarray are typically spaced about one micron apart. The volume of one of these tiny wells can be on the order of a femtoliter (1.0×10−15 liter).
One problem that arises when using microarrays is that many of the beads are not correctly placed or centered in the wells. A common method used to place the beads into the wells is to introduce beads onto the surface of the microarray within a fluid, and rock the array back and forth until the fluid pushes the beads into the wells. This method tends to be tedious and ineffective, typically resulting in only about 70% of the beads seating correctly in the wells. Another problem is that the washing step tends to lift about 5-10% of the beads back out of the wells. Therefore, what is needed to improve the yield and efficiency of DNA experiments is a DNA microarray that can successfully capture and retain close to 100% of the beads in the wells.